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Message-ID: <20250211092604.15160-1-luis@igalia.com>
Date: Tue, 11 Feb 2025 09:26:04 +0000
From: Luis Henriques <luis@...lia.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Matt Harvey <mharvey@...ptrading.com>,
	Bernd Schubert <bschubert@....com>,
	Joanne Koong <joannelkoong@...il.com>,
	Luis Henriques <luis@...lia.com>
Subject: [PATCH v4] fuse: add new function to invalidate cache for all inodes

Currently userspace is able to notify the kernel to invalidate the cache
for an inode.  This means that, if all the inodes in a filesystem need to
be invalidated, then userspace needs to iterate through all of them and do
this kernel notification separately.

This patch adds a new option that allows userspace to invalidate all the
inodes with a single notification operation.  In addition to invalidate
all the inodes, it also shrinks the sb dcache.

Signed-off-by: Luis Henriques <luis@...lia.com>
---
* Changes since v3
- Added comments to clarify semantic changes in fuse_reverse_inval_inode()
  when called with FUSE_INVAL_ALL_INODES (suggested by Bernd).
- Added comments to inodes iteration loop to clarify __iget/iput usage
  (suggested by Joanne)
- Dropped get_fuse_mount() call -- fuse_mount can be obtained from
  fuse_ilookup() directly (suggested by Joanne)

(Also dropped the RFC from the subject.)

* Changes since v2
- Use the new helper from fuse_reverse_inval_inode(), as suggested by Bernd.
- Also updated patch description as per checkpatch.pl suggestion.

* Changes since v1
As suggested by Bernd, this patch v2 simply adds an helper function that
will make it easier to replace most of it's code by a call to function
super_iter_inodes() when Dave Chinner's patch[1] eventually gets merged.

[1] https://lore.kernel.org/r/20241002014017.3801899-3-david@fromorbit.com

 fs/fuse/inode.c           | 83 +++++++++++++++++++++++++++++++++++----
 include/uapi/linux/fuse.h |  3 ++
 2 files changed, 79 insertions(+), 7 deletions(-)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index e9db2cb8c150..5aa49856731a 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -547,25 +547,94 @@ struct inode *fuse_ilookup(struct fuse_conn *fc, u64 nodeid,
 	return NULL;
 }
 
+static void inval_single_inode(struct inode *inode, struct fuse_conn *fc)
+{
+	struct fuse_inode *fi;
+
+	fi = get_fuse_inode(inode);
+	spin_lock(&fi->lock);
+	fi->attr_version = atomic64_inc_return(&fc->attr_version);
+	spin_unlock(&fi->lock);
+	fuse_invalidate_attr(inode);
+	forget_all_cached_acls(inode);
+}
+
+static int fuse_reverse_inval_all(struct fuse_conn *fc)
+{
+	struct fuse_mount *fm;
+	struct super_block *sb;
+	struct inode *inode, *old_inode = NULL;
+
+	inode = fuse_ilookup(fc, FUSE_ROOT_ID, &fm);
+	if (!inode || !fm)
+		return -ENOENT;
+
+	iput(inode);
+	sb = fm->sb;
+
+	spin_lock(&sb->s_inode_list_lock);
+	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+		spin_lock(&inode->i_lock);
+		if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
+		    !atomic_read(&inode->i_count)) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+
+		/*
+		 * This __iget()/iput() dance is required so that we can release
+		 * the sb lock and continue the iteration on the previous
+		 * inode.  If we don't keep a ref to the old inode it could have
+		 * disappear.  This way we can safely call cond_resched() when
+		 * there's a huge amount of inodes to iterate.
+		 */
+		__iget(inode);
+		spin_unlock(&inode->i_lock);
+		spin_unlock(&sb->s_inode_list_lock);
+		iput(old_inode);
+
+		inval_single_inode(inode, fc);
+
+		old_inode = inode;
+		cond_resched();
+		spin_lock(&sb->s_inode_list_lock);
+	}
+	spin_unlock(&sb->s_inode_list_lock);
+	iput(old_inode);
+
+	shrink_dcache_sb(sb);
+
+	return 0;
+}
+
+/*
+ * Notify to invalidate inodes cache.  It can be called with @nodeid set to
+ * either:
+ *
+ * - An inode number - Any pending writebacks within the rage [@offset @len]
+ *   will be triggered and the inode will be validated.  To invalidate the whole
+ *   cache @offset has to be set to '0' and @len needs to be <= '0'; if @offset
+ *   is negative, only the inode attributes are invalidated.
+ *
+ * - FUSE_INVAL_ALL_INODES - All the inodes in the superblock are invalidated
+ *   and the whole dcache is shrinked.
+ */
 int fuse_reverse_inval_inode(struct fuse_conn *fc, u64 nodeid,
 			     loff_t offset, loff_t len)
 {
-	struct fuse_inode *fi;
 	struct inode *inode;
 	pgoff_t pg_start;
 	pgoff_t pg_end;
 
+	if (nodeid == FUSE_INVAL_ALL_INODES)
+		return fuse_reverse_inval_all(fc);
+
 	inode = fuse_ilookup(fc, nodeid, NULL);
 	if (!inode)
 		return -ENOENT;
 
-	fi = get_fuse_inode(inode);
-	spin_lock(&fi->lock);
-	fi->attr_version = atomic64_inc_return(&fc->attr_version);
-	spin_unlock(&fi->lock);
+	inval_single_inode(inode, fc);
 
-	fuse_invalidate_attr(inode);
-	forget_all_cached_acls(inode);
 	if (offset >= 0) {
 		pg_start = offset >> PAGE_SHIFT;
 		if (len <= 0)
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 5e0eb41d967e..e5852b63f99f 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -669,6 +669,9 @@ enum fuse_notify_code {
 	FUSE_NOTIFY_CODE_MAX,
 };
 
+/* The nodeid to request to invalidate all inodes */
+#define FUSE_INVAL_ALL_INODES 0
+
 /* The read buffer is required to be at least 8k, but may be much larger */
 #define FUSE_MIN_READ_BUFFER 8192
 

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